009A Sample Midterm 2, Problem 4 Detailed Solution

To determine drug dosages, doctors estimate a person's body surface area (BSA) (in meters squared) using the formula:

${\text{BSA}}={\frac {\sqrt {hm}}{60}}$

where  $h$  is the height in centimeters and  $m$  is the mass in kilograms. Calculate the rate of change of BSA with respect to height for a person of a constant mass of  $m=85.$  What is the rate at  $h=170$  and  $h=190?$  Express your results in the correct units. Does the BSA increase more rapidly with respect to height at lower or higher heights?

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Background Information:
Power Rule
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{d}{dx}(x^n)=nx^{n-1}}

Solution:

Step 1:
First, we have  Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle m=85.}
So, we have
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \begin{array}{rcl} \displaystyle{\text{BSA}} & = & \displaystyle{\frac{\sqrt{85h}}{60}}\\ &&\\ & = & \displaystyle{\frac{\sqrt{85}\sqrt{h}}{60}.} \end{array}}

Step 2:
Now, using the Power Rule, we get
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \begin{array}{rcl} \displaystyle{\frac{d(\text{BSA})}{dh}} & = & \displaystyle{\frac{\sqrt{85}}{60}\cdot \frac{1}{2} h^{-1/2}}\\ &&\\ & = & \displaystyle{\frac{\sqrt{85}}{120\sqrt{h}}.} \end{array}}

Step 3:
For  Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle h=170,}   we get
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{d(\text{BSA})}{dh}=\frac{\sqrt{85}}{120\sqrt{170}} \text{ m}^2\text{/cm}.}
For  Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle h=190,}   we get
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{d(\text{BSA})}{dh}=\frac{\sqrt{85}}{120\sqrt{190}} \text{ m}^2\text{/cm}.}

Step 4:
Since  Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle h}   is in the denominator of the formula for  Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{d(\text{BSA})}{dh},}
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \text{BSA}}   increases more rapidly with respect to height at lower heights.

Final Answer:
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{d(\text{BSA})}{dh}=\frac{\sqrt{85}}{120\sqrt{h}}}
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{\sqrt{85}}{120\sqrt{170}} \text{ m}^2\text{/cm}}
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{\sqrt{85}}{120\sqrt{190}} \text{ m}^2\text{/cm}}
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \text{BSA}}   increases more rapidly with respect to height at lower heights.

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